/Engine/Source/Editor/GameProjectGeneration/Public/ClassTemplateEditorSubsystem.h
Reads the source template text from disk. If failure to read from disk, returns false and provides text reason.
bool ReadSource ( [FString](API\Runtime\Core\Containers\FString) & OutSourceFileText, [FText](API\Runtime\Core\Internationalization\FText) & OutFailReason ) const